Portable personal computing devices such as Smartphones, Personal Digital Assistants (PDAs), portable computers, tablet computers and audio devices such as digital music players have become ubiquitous in recent years. These devices usually have different built-in physical electrical interfaces such as USB, FireWire, RS232 serial port and audio plug, among others. In almost all of these devices, and in particular in the audio devices, the audio plug is a common interface. The audio plug of a device acts as a receptacle for an audio jack connector which is used for transmitting analog signals including audio signals. The audio plug is used to connect to headphones, speakers, microphones, and hands-free devices, among others.
In the past, many mobile phones used to have their own proprietary form of audio plugs configured to be used with cables outfitted with matching proprietary audio jacks. However, recently the functionality of mobile phones has changed so much that most mobile phones are now also digital music players, payment devices, navigation devices and cameras, among others. Additional accessory devices including headphones, printers, and card readers, among others, may be connected to the mobile phones in order listen to music, print and complete payments, among others. Therefore, due to these added functionalities and the need to connect additional accessory devices to mobile phones, 2.5 mm audio plugs and/or 3.5 mm audio plugs can now be found on most middle to high-end mobile phones.
Besides wired connections, many portable devices are equipped with wireless connection capabilities such as Bluetooth, Wi-Fi or WiMAX, among others. In a wired connection where the devices are physically connected, the data security is less of a concern. Unlike wired connections, eavesdropping is possible in wireless connections and the data must be cryptographically protected and the two communicating devices must be authenticated with one another. A pairing process is necessary to establish this secure connection.
Bluetooth is a proprietary low-powered wireless technology for short-distance communication. The characteristics of Bluetooth make it a competitive candidate for data communication technology between a host device and other peripheral devices. Before the two devices can communicate, a pairing process has to be done first to establish a secure connection between the two Bluetooth devices. In the pairing process, the devices exchange and establish their common link keys used for the secure connection. The link keys are stored and further connections can be done without user interaction.
The number of devices equipped both with an audio plug interface and Bluetooth technology is expected to increase rapidly. The audio interface can be used for data transfer but the data rate is limited. Bluetooth can support a higher data rate but it is preferable to keep the Bluetooth transceiver off to save power and reduce radiation. Accordingly, there is a need for a simple and efficient way to enable wireless device pairing where control side information is communicated through an alternative channel.